1. Field of the Invention
The present invention relates to a transistor digital logic circuit and, more particularly, to the prevention of saturation in bipolar transistor digital logic circuits so as to achieve fast switching.
2. Description Relative to the Prior Art
In digital logic circuits it is highly desirable to be able to switch from one output state to the other, especially when such circuits are used in memory configurations where circuit speed is a critical factor. To obtain a fast turn-on transition, high base drive currents are used. However, a high base drive current causes the transistor to deeply saturate and store excessive base charge. This base charge has to be removed when the transistor is to be turned off and results in a long turn-off delay.
To prevent saturation, which occurs when the collector to emitter voltage of a transistor drops below about 0.1 volt, some prior art circuits have used a Schottky barrier diode in shunt with the base-collector junction of the transistor to clamp the voltage across the base-collector junction at a relatively low forward level. The disadvantage of this structure is that additional process complexity is required in making Schottky diodes.